Propellent powder



Patented JulylG, 1957 ice PRGPELLEN T POWDER Ralph L. Cook, Alton, Ill., assignor to Olin Mathieson Chemical Corporation, East Alton, 111., a corporation oEVirginia No Drawing. Application January 24, 1956, Serial No. 561,374

9 Claims. (Cl. 52-11) This invention relates to explosives and in particular to propellent powders having improved ballistic characteristics.

In the manufacture of smokeless powder, large batches of the product having ballistic properties in the desired range are prepared and the powder is then adjusted to i the particular ballistic level required. This adjustment is 1 normally accomplished by impregnating the powder grains with a deterrent such as dinitrotoluene to reduce its ballistic level or with an accelerator such as nitroglycerine to increase its potential. Powder having a desired ballistic level can also be prepared with a fair degree of success by blending a relatively slow powder. with a relatively'fastv powder. Conventionally, powders of such varying ballistic characteristics have been prepared by changes in grain size, shape, density and composition, or by relocation of potential modifiers. Thus, it has often proven necessary or desirable to keep on hand stocks of powders of varying physical or chemical description.

.Probleinsv always exist in assuring that such diverse materials are blended uniformly and that variations in ballistic properties do not exist throughout the batch. Thus, all of the prior art methods for adjusting the ballistic properties of smokeless powder have been inadequate in spite of the fact that they involved additional expensive processing.

It is therefore an object of this invention to provide a novel method of adjusting the ballistic properties of propellent powder that overcomes the disadvantages of the prior art. Another object of this invention is to pro vide a novel propellent powder having. improved ballistic properties. A further object of this invention is to provide a process for balancing the charge weight, pressure and velocity of propellent powder without re-working the powder or altering its base composition.

The above objects as well as others which will become apparent from the following description are achievedin' accordance with this invention, generally speaking, by providing a powder charge whose grains are surface coated. with finely divided potassium. nitrate or sodium nitrate and a finely divided inorganic crystalline ballistic in-. hibitor. Ballistic inhibitors that have been found suitable for use in accordance with this invention include inorganic salts, such as barium nitrate, lithium nitrate, potassium sulfate, barium suifate, lithium sulfate, sodium sulfate, potassium carbonate, lithium carbonate and calcium carbonate. It is generally preferred to use potas sium nitrate and potassium sulfate to attain the. ends of this invention because these potassium salts, in addition to their ballistic balancing effect, also have a marked tendencytoinhibit the flash of the powder upon firing. In accordance with this invention it is. generally Preferred to coat each ofv the grains in. the powder charge with a mixture of the nitrate of potassium or sodium and one or more of. the ballistic inhibitors. In some cases, however, instead of applying a. mixture of the salts to each of. the. powder grains, one. portion of the. charge. can be coated with one. of the. nitrates .and blended with a= powder inhibitors. It has been found that the addition of sodium nitrate or potassium nitrate to the grain surface tends to reduce the weight of powder required in any given round to produce a given velocity and at the same time tends to increase the pressure at which this velocity is achieved. On the other hand, it has been found that the addition of potassium sulfate or one of the other ballistic inhibitors to the grain surface tends to increase the weight of powder required in any given round to produce a given velocity and at the same time tends to reduce the pressure at which this velocity is achieved. By combining the properties of potassium nitrate or sodium nitrate and the action of the ballistic inhibitors in one powder load it has been found that the charge weight, pressure and velocity of the resultant powder can be adjusted within wide limits. The potassium salts applied to the surface of the powder grains in accordance with this invention must be very finely divided and iii-order to be effective their granulation must be less than about 325 mesh, U. S. Tyler screen, or in other Words, less than about 44 microns.

The ratio of potassium nitrate or sodium nitrate to the ballistic inhibitor has a very definite effect on the degree of ballistic change. These ratios can of course vary within Wide limits and are dependent upon the ballistic level desired. In most instances, however, it is preferred to use mixtures of these salts in which the ratio of solium nitrate or potassium nitrate to the ballistic inhibitor is between about 4:1 and 1:4. The modifying elfect of these salts is also a function of the concentration of the salt mixture on the grain. surface. The effective range of the-salt concentration based on the weight of the powder is between about: 0.10 percent and about 1.50 percent; anditheeflect is most pronounced when this concentrationis between about 0.4 percent and about 1.0 percent. While amounts of the salts below 0.10 percent may have some influence on the ballistic properties of the powder, their effect is not'ineasurable and is considered to be insignificant. Effects obtained by use of the mixed salt coating increase markedly up to about 1.00 percent total salt content based on the weight of the powder. The addition of these saltsin excess of 1.50 percent generally lowers the ballistic level of the powder and such excessive addition merely results from the adulteration of the powder with a non-explosive component.

By way of example, substantially spherical powder grains formed in accordance with the process disclosed in U. S. 2,160,626 were provided with surface coatings of potassium nitrate and potassium sulfate by the following method. These grains were composed of about 83 percent nitrocellulose having a nitrogen content of about 13.15 percent, 10 percent nitroglycerine, 6 percent dibutylphthalate and l percent'diphenylamine. One thou sand (1000) parts by weight of these powder grains were placed in a Sweetie or' tumbling barrel and provided with a coating of potassium salts having a granulation of 325 mesh by pouring a suspension of potassium nitrate and potassium sulfate in isopropyl alcohol over the powder. This suspension'was composed of about 5 parts potassium nitrate, 5 parts potassium sulfate, 2 /2 parts dibutylphthalate, 0.05 part d'phenylamine, 0.07 part calcium carbonate, 0.05 part ethylcellulose and 20' parts isopropyl alcohol. All proportions being expressed in parts by weight based on the weight of the powder. In this'suspension the isopropyl alcohol serves as the carrier while the dibutylphthalate softens the surface of the grain and insures the adhesion of the salt thereto. The diphenylamine and calcium carbonate have a stabilizing influence on the powder while the ethylcellulose serves a'sa surface active agent. The mixture of powder and thesalt suspension was thentumbled for about one hour at 50 C. or until a substantially uniform coating of the salt mixture had been applied to the surface of the grains. Tumbling was continued at this temperature for another 45 minutes during which time the isopropyl alcohol was removed. The resultant powder had an adherent surface coating of 0.35 percent potassium nitrate and 0.35 percent potassium sulfate. In like manner, another portion of this powder was provided with a coating of 0.6 percent potassium nitrate and still another portion of the powder was provided with a coating of 0.6 percent potassium sulfate.

Powder grains coated in accordance with the foregoing process and having a diameter between 0.020" and 0.025" were charged into 27 mm. cartridges and fired in comparison with substantially identical cartridges charged with the same base powder that was not provided with a surface coating of the salts. The results obtained upon firing these cartridges is set forth in Table I wherein the charge weight is set forth in grains, the pressure in the gun barrel in pounds per square inch and the velocity of the projectile in feet per second.

As indicated in the foregoing table, the base powder not having a salt coating had a very satisfactory velocity of 2655 ft. per second but it developed a gun barrel pressure in excess of 38,000 p. s. i. which is the absolute maximum pressure allowable for the round. By the addition of 0.60 percent potassium nitrate as indicated by the second entry in the table, the pressure was increased beyond all reasonable limits to 50,300 p. s. i. but the velocity was reduced almost 70 ft. per second to a value of only 2587 which is below accepted specifications for this round of ammunition. By contrast, cartridges loaded with a larger charge weight of powder coated with potassium sulfate produced a pressure less than 33,000 p. s. i. and a velocity of 2626 ft. per second, both of which are below specifications. The last entry in the table which is directed to a powder coated with a mixture of potassium nitrate and potassium sulfate represents a preferred embodiment of this invention. By providing powder with such a coating it will be noted that the pressure developed was reduced from over 38,000 to 36,500 p. s. i. while the charge weight was increased grains and the cartridge upon firing had a velocity of 2650 ft. per second. Thus, by the simple expedient of coating the powder with a mixture of these salts, the pressure was reduced 1700 p. s. i. to a point well within specifications and the velocity was maintained practically constant.

In accordance with another embodiment of this invention, substantially spherical powder grains of the type used above but containing 7.75 percent dibutylphthalate as a deterrent and having a diameter between about 0.025" and 0.034" were provided with mixed coatings of potassium nitrate and potassium sulfate in accordance with the procedure used in the above example. One portion of the powder was coated with 0.67 percent potassium nitrate and 0.33 percent potassium sulfate while another portion of the powder was provided with a salt coating in which the proportions of the nitrate and sulfate were reversed. These coated powders were loaded into mm. cartridges and fired and their ballistic performance was compared with identical cartridges loaded with the same powder without the salt coating. The results of these firing tests are set forth in Table II.

The uncoated powder as originally prepared provided the projectiles with a velocity of 2465 which is slightly below specifications for this round of ammunition. This deficiency in velocity was overcome as indicated in the table by coating the powder with a mixture of potassium nitrate and potassium sulfate in which. the ratio of the former to the latter was about 2:1 but the pressure of 42,400 p. s. i. thus obtained was considered to be slightly excessive. As shown in the last entry in the table, the velocity was adjusted to an acceptable value of 2489 ft. per second with a barrel pressure of 35,900 p. s. i. when the charge weight was increased only 10 grains.

From the above examples it is clear that the present invention provides a novel method for controllably changing the ballistics of a given base propellent powder so that the final speed and pressure adjustment can be accomplished by merely providing the powder with a mixed coating of potassium nitrate or sodium nitrate and a ballistic inhibitor such as potassium sulfate rather than by coating the powder with modifiers such as nitroglycerine or dinitrotoluene or by rolling the powder. Although it is not specifically set forth in the above embodiments it is self-evident that, when desired, the charge weight of the powder load in specific cartridges can be raised or lowered without sacrificing the requirements for pressure developed and velocity imparted to the projectile. While the above examples specify potassium nitrate and potassium sulfate as the materials used to control the ballistic characteristics of the powder, it will be realized that sodium nitrate can be used in place of the potassium nitrate and that the other ballistic inhibitors referred to above may be used in place of the potassium sulfate.

Potassium nitrate, potassium sulfate and other salts have heretofore been incorporated into gelatinized powder grains in order to reduce the flash of the powder, but this invention is not concerned with powders containing such incorporated salts and such incorporation of the salts into the body of the powder grain does not provide a method of controlling the ballistic balance of the powder. It has been ascertained that this phenomenon of ballistic control is limited to surface coatings, and that the introduction of the salts into the body of the grains does not bring about the ballistic control contemplated by the present invention.

The powder grains provided by this invention and one method of making them have been described in considerable detail in the foregoing for the purpose of illustration. It is of course to be understood that any suitable process for coating the grains can be utilized and that various liquid carriers can be substituted for the isopropyl alcohol. For example, any relatively volatile liquid which is a non-solvent for the smokeless powder and for the salts may be used. Such liquids include ethyl alcohol, methyl alcohol, benzene, toluene, gasoline and the like. Although the invention was described with particular reference to substantially spherical powder grains formed by the process set forth in U. S. Patents 2,027,114 and 2,160,626, the coating of this invention can be used to advantage on powder grains made by other processes such as by extrusion and the like and on grains of any suitable size and shape.

The salt coating of this invention can be advantageously applied to smokeless powder grains having a base of nitrocellulose, nitrocellulose and accelerators, nitrocellulose and deterrents, nitrocellulose-nitroglycerine with deterrents, as well as other similar gelatinizable polynitro compounds such as nitrostarch and polyvinyl nitrate.

Many other variations in the invention will occur to those skilled in the art and can be used without departing from the spirit and scope of this invention except as it is limited by the appended claims.

What is claimed is:

l. A smokeless powder grain having a surface coating of a mixture of about 1 part to about 4 parts by weight of potassium sulfate and about 4 parts to about 1 part by weight of a nitrate selected from the group of alkaline metal nitrates consisting of the nitrates of potassium and sodium, the coating being between about 0.10 percent and about 1.50 percent based on the weight of the powder.

2. A smokeless powder grain having a surface coating of a mixture of finely divided potassium nitrate and potassium sulfate, the coating being between about 0.10 percent and about 1.50 percent based on the weight of the powder, and the weight ratio of potassium nitrate to potassium sulfate being between about 4:1 and 1:4.

3. A substantially spherical smokeless powder grain having a surface coating of a mixture of from about 1.2 percent to about 0.3 percent by weight potassium nitrate and from about 0.3 percent to about 1.2 percent by weight potassium sulfate.

4. A propellent powder charge comprising smokeless powder grains having a surface coating of potassium nitrate together with smokeless powder grains having a surface coating of the potassium sulfate, the combined weight of the potassium nitrate and potassium sulfate being between 0.10 percent and 1.50 percent of the powder charge, and the weight ratio of potassium nitrate to potassium sulfate being between about 4:1 and 1:4.

5. A propellent powder charge comprising smokeless powder grains having a surface coating of a nitrate of an alkaline metal selected from the group consisting ofpotassium and sodium together with smokeless powder grains having a surface coating of an inorganic salt ballistic inhibitor selected from the group consisting of barium nitrate, lithium nitrate, potassium sulfate, barium sulfate, lithium sulfate, sodium sulfate, potassium carbonate, lithium carbonate and calcium carbonate, the combined weight of the coatings being between about 0.10 percent and 1.5 percent of the powder charge, and the weight ratio of the nitrate of the alkaline metal to the inorganic salt ballistic inhibitor being between about 4:1 and 1:4.

6. A propellent powder charge comprising smokeless powder grains having a surface coating of a nitrate of an alkaline metal selected from the group consisting of potassium and sodium together with smokeless powder grains having a surface coating of an inorganic salt ballistic inhibitor selected from the group consisting of barium nitrate, lithium nitrate, potassium sulfate, barium sulfate, lithium sulfate, sodium sulfate, potassium carbonate, lithium carbonate and calcium carbonate, the combined weight of the coatings being between about 0.40 percent and 1.0 percent of the powder charge, and the weight ratio of the nitrate of the alkaline metal to the inorganic salt ballistic inhibitor being between about 4:1 and 1:4.

7. A method of controlling the ballistic properties of propellent powder grains comprising coating said grains with a mixture of a nitrate of an alkaline metal selected from the group consisting of potassium and sodium and of a crystalline inorganic salt ballistic inhibitor selected from the group consisting of barium nitrate, lithium nitrate, potassium sulfate, barium sulfate, lithium sulfate, sodium sulfate, potassium carbonate, lithium carbonate and calcium carbonate, the coating being between about 0.10 percent and about 1.5 percent based on the weight of the powder, and the weight ratio of the nitrate of the alkaline metal to the inorganic salt ballistic inhibitor being between about 4:1 and 1:4.

8. A method of improving the ballistic properties of propellent powder grains comprising coating said grains I with about 0.10 percent to about 1.50 percent of a mixture of about 4 parts to about 1 part by weight of potassium nitrate and about 1 part to about 4 parts by weight of potassium sulfate.

9. A smokeless powder grain having a surface coating of a mixture of a nitrate of an alkaline metal selected from the group consisting of potassium and sodium and an inorganic salt ballistic inhibitor selected from the group consisting of barium nitrate, lithium nitrate, potassium sulfate, barium sulfate, lithium sulfate, sodium sulfate, potassium carbonate, lithium carbonate, and calcium carbonate, the coating being between about 0.10 percent and about 1.50 percent based on the weight of the powder and the weight ratio of the nitrate of the alkaline metal to the inorganic salt ballistic inhibitor being between about 4:1 and 1:4.

No references cited. 

1. A SMOKELESS POWER GRAIN HAVING A SURFACE COATING OF A MIXTURE OF ABOUT 1 PART TO ABOUT 4 PARTS BY WEIGHT OF POTASSIUM SULFATE AND ABOUT 4 PARTS TO ABOUT 1 PART BY WEIGHT OF A NITRATE SELECTED FROM THE GROUP OF ALKALINE METAL NITRATEDS CONSISTING OF THE NITRATES OF POTASSIUM AND SODIUM, THE COATING BEING BETWEEN ABOUT 0.10 PERCENT AND ABOUT 1.50 PERCENT BASED ON THE WEIGHT OF THE POWER. 